<style>
input:checked {
  appearance: none;
}
input:required {
  border-bottom-style: groove;
}
</style>
<script>
document.addEventListener("DOMContentLoaded", () => {
  a.getBoundingClientRect();
  a.defaultChecked = true;
  a.getBoundingClientRect();
})
</script>
<input id="a" required="required" type="radio">
